Bi-curvature lens for light emitting diodes and photo detectors

ABSTRACT

A bi-curvature lens for diodes in an infrared wireless communication transceiver is disclosed. Devices having such a bi-curvature lens, such as a light emitting device, a light detecting device, and a transceiver are also disclosed. A method for designing such a lens, and a method for fabricating a device having such a lens are also disclosed. The bi-curvature lens disclosed has a bottom hemispherical portion and a top aspherical portion. Light emitting diodes and photo detectors used in conjunction with bi-curvature lenses display symmetrical radiation intensity profiles, in accordance with Infrared Data Association standards and protocols.

FIELD OF THE INVENTION

Embodiments of the present invention pertain generally to wirelesscommunication devices. More specifically, embodiments of the presentinvention pertain to lenses used with light emitting diodes (LED) orLEDs chip/die and photo detectors (PD) or PDs chip/die in wirelesscommunication devices.

BACKGROUND OF THE INVENTION

Light emitting diodes (LEDs) and photo detectors are widely used with orwithout lenses to facilitate wireless infrared communication in devicessuch as laptop computers, personal digital assistants, printers, mobilephones, modems, digital pagers, electronic cameras, and hand-heldcomputers. The growing popularity of wireless communication has placed atremendous demand for small form factor for components such astransceivers within wireless communication devices.

In a typical wireless communication device, an infrared transmitter(e.g. an LED chip/die with lens) is arranged adjacent to an infraredreceiver (e.g. a photo detector chip/die) in an arrangement called atransceiver. An embedded LED chip/die with lens is called an emitter. Anembedded PD die/chip with lens is called a transmitter. The transmitterand the receiver are connected with an integrated circuit for signalprocessing. On the surface of the transceiver, there are two lenses. Alight emitting diode chip/die is located in or near the center of one ofthe lenses, and a photo detector chip/die is located in or near thecenter of the other lens. Conventionally, spherical lenses 110 describedby a radius r (115), as depicted in FIG. 1, are employed to ensureproper directional distribution of light.

One method of evaluating LED lenses is the generation of a radiantintensity profile. The radiant intensity profile indicates flux ofradiation per steradian of the surface of a lens. The term flux, in thiscontext, refers to the energy per steradian of the emission of the LED.A steradian 210 is a three dimensional unit of spherical geometry,depicted in FIG. 2. One steradian 210 is a solid angle, e.g. a conethat, having its vertex 221 in the center of a sphere 201 of radius r(205), cuts off an area (220) on the surface of the sphere equal to thatof a square with sides of length equal to the radius r of the sphere. Inother words, one steradian 210 is a solid angle defining an area 220equal to r² on the surface of a sphere 201 described by radius r (205).

A radiant intensity profile for a spherical lens is presented in FIG. 3.The curve of flux per steradian in a horizontal direction 310 issubstantially symmetrical about the maximum 330. The curve of flux persteradian in a vertical direction 320 is also substantially symmetricalabout the maximum 330. This symmetry in both the vertical and horizontaldirections is required to satisfy the standards and protocols of theInfrared Data Association (IrDA), a non-profit organization dedicated todeveloping globally adopted specifications for infrared wirelesscommunication. As can be appreciated, it is desirable for a commerciallyavailable device to conform to IrDA standards and protocols.

One approach to meeting the current demand for smaller components withinwireless devices is to manufacture smaller spherical lenses for use withLEDs and photo detectors in infrared transceivers. However, as thediameter is decreased for spherical lenses used with LEDs, thebrightness of the LEDs decreases, therefore signal output iscompromised. As the diameter is decreased on spherical lenses used withphoto detectors, less light is received at the photo detector, thereforesignal processing is compromised.

SUMMARY OF THE INVENTION

Embodiments of the present invention, a light emitting device having alight emitting diode chip/die and a bi-curvature dome lens aredisclosed. The bi-curvature dome lens according to embodiments of thepresent invention has a hemispherical bottom portion defined by a firstradius and an aspherical upper portion defined by a second radius and aconic constant.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are incorporated in and form a part ofthis specification, illustrate embodiments of the invention and,together with the description, serve to explain the principles of theinvention:

FIG. 1 is an illustration of a conventional spherical dome lens for anLED chip/die.

FIG. 2 illustrates a steradian.

FIG. 3 is a radiant intensity profile of a conventional spherical domelens with an LED chip/die.

FIG. 4 depicts a bi-curvature dome lens in accordance with embodimentsof the present invention.

FIG. 5 is a radiant intensity profile of a bi-curvature dome lens inaccordance with embodiments of the present invention.

FIG. 6 depicts a light emitting device with a bi-curvature dome lens inaccordance with embodiments of the present invention.

FIG. 7 depicts a light receiving device with a bi-curvature dome lens inaccordance with embodiments of the present invention.

FIG. 8 illustrates a transceiver having bi-curvature dome lenses inaccordance with embodiments of the present invention.

FIG. 9 is a flowchart reciting steps in a method of designing abicurvature dome lens.

FIG. 10 is a flowchart illustrating steps in a method of fabricating anemitter and/or receiver LED and/or photo detector device disclosed inthe present invention.

DETAILED DESCRIPTION

Reference will now be made in detail to various embodiments of theinvention, examples of which are illustrated in the accompanyingdrawings. While the invention will be described in conjunction withvarious embodiments, it will be understood that they are not intended tolimit the invention to these embodiments. On the contrary, the inventionis intended to cover alternatives, modifications and equivalents, whichmay be included within the spirit and the scope of the invention asdefined by the appended claims. Furthermore, in the following detaileddescription of the present invention, numerous specific details are setforth in order to provide a thorough understanding of the presentinvention. However, it will be apparent to one skilled in the art thatthe present invention may be practiced without these specific details.In other instances, well-known methods, procedures, components,structures and devices have not been described in detail so as to avoidunnecessarily obscuring aspects of the present invention.

One embodiment of the present invention is a bi-curvature dome shapedlens 400, depicted in FIG. 4. The profile of a bi-curvature lens isdefined by two curvatures, hence the term “bi-curvature.” As illustratedin FIG. 4, the bottom portion 410 of the dome 400 has a hemisphericalcontour 411, and radius r1 (415). The top portion 420 has an asphericcontour 421, a radius of curvature r2 (425) and a conic constant k. Theconic constant k is a function of the eccentricity of the asphericcontour, where the eccentricity defines the deviation from spherical ofthe aspherical contour. For a sphere, the conic constant is zero. Theterm aspherical, in this context, refers to a surface or contour that isnot spherical, e.g. the conic constant is not equal to zero. In oneembodiment, the aspherical contour 421 is an elliptical contour.

FIG. 5 illustrates a radiant intensity profile 500 of the lightdistribution of an LED having a bi-curvature lens (as in FIG. 4)according to embodiments of the present invention. The flux per steradian in the horizontal direction (510) is symmetrical about the maximum530. The flux per sterad ian in the vertical direction (520) is alsosymmetrical about he maximum 530. Symmetry about the maximum in both thehorizontal and vertical directions of radiant intensity is required tosatisfy Infrared Data Association (IrDA) standards and protocol.

Referring now to FIG. 6, a bi-curvature lens 601 can be used to directlight 610 emitted from a light emitting diode chip/die 620, e.g. aninfrared emitting device, according to one embodiment of the presentinvention. A bi-curvature lens 701 according to embodiments of thepresent invention can also be used to direct light 710 for detection ata photo detector 720, as illustrated in FIG. 7. In one embodiment, thephoto detector 720 depicted in FIG. 7 is a photo detector chip, and inanother embodiment, the photo detector 720 depicted in FIG. 7 is a photodetector die. A bi-curvature dome lens in accordance with embodiments ofthe present invention could be employed to guide any wavelength ofvisible light, infrared light, ultraviolet, or other light. Lighttransmitted through a bi-curvature dome lens in accordance withembodiments of the present invention will display symmetry of radiantintensity along the horizontal and the vertical directions, as requiredby the IrDA.

The diameter of a lens in accordance with the present invention can besmaller than the diameter of a conventional spherical lens. Thus, atransceiver having bi-curvature lenses can be smaller and more compactthan a transceiver having spherical lenses. A wireless communicationdevice having transceivers with bi-curvature lenses can be smaller andmore compact than a wireless communication device having transceiverswith conventional spherical lenses.

FIG. 8 illustrates a wireless communication transceiver 800, in oneembodiment an infrared wireless communication transceiver. An LED chip820 is attached with a PCB substrate 810 by a bondable wire 821. A photodetector chip 830 is attached with PCB substrate 810 by a bondable wire831. A layer of epoxy 840 covers the LED chip 820 and the photo detectorchip 830. Light 865 emitted by the LED chip 820 is transmitted through abi-curvature lens 860 to produce symmetrical radiant intensity in boththe horizontal and vertical directions, as illustrated by the radiantintensity profile of FIG. 5. Light 855 transmitted through abi-curvature lens 850 in accordance with the present invention isreceived at the photo detector chip 830.

One embodiment of the present invention is the design method employed toobtain a bi-curvature dome capable of emitting light of symmetricalradiant intensity, in both the horizontal and the vertical directions.One design method is recited in flowchart 900 of FIG. 9. Initially, aspherical structure, e.g. a hemispherical structure, is simulated forthe bottom portion (410 in FIG. 4) of the bi-curvature lens (400 in FIG.4), as in step 910. A sequential ray trace program can then be employedto develop an aspheric contour (421 in FIG. 4) for the top portion (420in FIG. 4) of the dome (400 in FIG. 4), as described in step 920 offlowchart 900. A subsequent step 930 is the simulation of a bi-curvaturedome (400 in FIG. 4) that combines the spherical bottom portion (410 inFIG. 4) simulated at step 910 and the aspherical top portion (420 inFIG. 4) simulated at step 920. Once the combination bi-curvature domestructure has been developed at step 930, a radiation intensity profile(e.g. FIG. 5) is simulated through the entire dome structure (400 inFIG. 4), as indicated by step 940 in flowchart 900. The radiationintensity profile simulated at step 940 is evaluated at step 950. Atstep 970, it is determined whether or not the radiation intensityprofile simulated at step 940 is desirable. The radiation intensityprofile simulated at step 940 is desirable if it is symmetric about amaximum in both the horizontal and the vertical directions, as in FIG.5. If the radiation intensity profile is satisfactory, the designprocess is done. If the radiation intensity profile is not satisfactory,e.g. not substantially symmetric about a maximum in both the horizontaland the vertical directions, certain parameters of the design can bealtered, as in step 960 in flowchart 900. For example, referring to FIG.4, the contour 421 of the aspheric portion 420 of the lens 400 could bemodified by increasing or decreasing the radius of curvature r2 425 orthe conic constant k. Another example of a parameter that can be alteredis the proportion of the bottom spherical portion 410 and the topaspherical portion 420 with respect to the height of the dome 400.According to an embodiment of the present invention, various iterationsare carried out until a desired radiant intensity distribution isobtained. Referring to flowchart 900, steps 940-970 are repeated untilsubstantially symmetry is achieved in the radiant intensity profilesimulated at step 940.

In one embodiment, a wireless communication transceiver is fabricated bya transfer mold method as recited in flowchart 1000 of FIG. 10.Initially, at least one diode chip, such as an LED chip (e.g. an IREDchip) or an infrared photo detector chip is attached to a printedcircuit board (PCB) substrate, as recited in step 1010. For atransceiver, an LED chip and a photo detector chip are attached to theprinted circuit board, adjacent to each other, as depicted in FIG. 8.Each chip is wire bonded to an electrical terminal of the PCB substrate.A layer of epoxy may be formed on the surface of the printed circuitboard substrate, covering the diode(s). Subsequently, as recited in step1020, the PCB substrate is located on a transfer mold fixture that hasmolds for bi-curvature lenses in accordance with embodiments of thebi-curvature dome lens of the present invention. Proceeding to step1030, an encapsulant is then cast to fill the bi-curvature lens mold,followed by a heat cure in step 1040 to ensure that the bi-curvaturedome lenses have the desired properties for light emission and/orreception. After a heat cure, the printed circuit board is ready to besingulated into individual light emitting units, photo detector units,or transceiver units, as recited in step 1050. Singulation of the PCBmay be accomplished by proper sawing.

It can be appreciated that the bi-curvature dome lens of the presentinvention can be formed from any material rendering efficient lighttransmission. A bi-curvature dome lens in accordance with embodiments ofthe present invention is not limited to infrared wireless communicationapplications. Embodiments of the present invention permit opticsdesigners to achieve desired radiant intensity profiles using very smalllenses, e.g. lenses having very small diameters. The cost of fabricationof bi-curvature lenses is comparable to the cost of fabrication ofconventional spherical lenses.

The foregoing description of specific embodiments of the presentinvention has been presented for purposes of illustration anddescription. They are not intended to be exhaustive or to limit theinvention to the precise forms disclosed, and many modifications andvariations are possible in light of the above teaching. The embodimentsof were chosen and described in order to best explain the principles ofthe invention and its practical application, to thereby enable othersskilled in the art to best utilize the invention and various embodimentswith various modifications as are suited to the particular usecontemplated. It is intended that the scope of the invention be definedby the claims appended hereto and their equivalents.

1. A light emitting device comprising: a light emitting diode; and abi-curvature dome lens, said lens comprising: a hemispherical portioncomprising a first radius; and an aspherical portion comprising a secondradius and a conic constant not equal to zero.
 2. The light emittingdevice of claim 1 wherein said hemispherical portion is a bottom portionof said dome and said aspherical portion is a top portion of said dome.3. The light emitting device of claim 1 wherein light emitted from saidlight emitting diode and transmitted through said bi-curvature lenscomprises a radiant intensity distribution, wherein said radiantintensity distribution is symmetrical in a horizontal angular directionand symmetrical in a vertical angular direction.
 4. The light emittingdevice of claim 1 wherein said light emitting diode is a light emittingchip, wherein said light emitting chip is embedded in said bi-curvaturedome lens.
 5. The light emitting device of claim 1 wherein said lightemitting diode is a light emitting die, wherein said light emitting dieis embedded in said bi-curvature dome lens.
 6. A light detecting devicecomprising: a photo detector; and a bi-curvature dome lens comprising: ahemispherical portion comprising a first radius; and an asphericalportion comprising a second radius and a conic constant not equal tozero.
 7. The light detecting device of claim 6 wherein said photodetector is a photo detector chip, wherein said photo detector chip isembedded in said bi-curvature dome lens.
 8. The light detecting deviceof claim 6 wherein said photo detector is a photo detector die, whereinsaid photo detector chip is embedded in said bi-curvature dome lens. 9.A method of emitting light comprising: producing light from a lightemitting diode; transmitting light through a bi-curvature lens, saidbi-curvature lens comprising a first hemispherical portion and a secondaspherical portion.
 10. A method of detecting light comprising:transmitting light through a bi-curvature lens, said lens comprising afirst hemispherical portion and a second aspherical portion; andreceiving light at a photo detector.
 11. A transceiver comprising: alight emitting device, said light emitting device comprising: a lightemitting diode; and a first bi-curvature lens, said first lenscomprising a hemispherical portion and an aspherical portion; and alight detecting device, said light detecting device comprising: a photodetector; and a second bi-curvature lens, said second lens comprising ahemispherical portion and an aspherical portion.
 12. The transceiver ofclaim 11 wherein said first bi-curvature lens is formed over a saidlight emitting diode and said second bi-curvature lens is formed oversaid photo detector by a transfer mold method.
 13. The transceiver ofclaim 1 1 wherein said first and second bi-curvature lenses distributeradiation symmetrically in a horizontal direction and a verticaldirection.
 14. The transceiver of claim 11 wherein said firsthemispherical portions of said first and second bi-curvature lensescomprise a first radius, and wherein said second aspherical portions ofsaid first and second bi-curvature lenses comprise a second radius and aconic constant not equal to zero.
 15. The transceiver of claim 11wherein said light emitting diode emits infrared light, and wherein saidphoto detector detects infrared light.
 16. The transceiver of claim 11wherein said light emitting diode is a light emitting chip, and whereinsaid light emitting chip is embedded in said first bi-curvature lens.17. The transceiver of claim 11 wherein said light emitting diode is alight emitting die, and wherein said light emitting die is embedded insaid first bi-curvature lens.
 18. The transceiver of claim 11 whereinsaid light detecting diode is a light detecting chip, and wherein saidlight detecting chip is embedded in said second bi-curvature lens. 19.The transceiver of claim 11 wherein said light detecting diode is alight detecting die, and wherein said light detecting chip is embeddedin said second bi-curvature lens.
 20. A method for fabricating awireless communication device on a printed circuit board substrate, saidmethod comprising: coupling a diode chip with said printed circuit boardsubstrate; and forming a lens over said diode chip, wherein said lenscomprises a bi-curvature contour.
 21. The method of claim 20 furthercomprising covering said diode chip with a layer of epoxy.
 22. Themethod of claim 20 wherein said bi-curvature contour comprises a firstspherical portion comprising a first radius, and a second asphericalportion comprising a second radius and a conic constant not equal tozero.
 23. The method of claim 20 wherein said first spherical portion isa bottom portion of said bi-curvature contour and said second asphericalportion is a top portion of said bi-curvature contour.
 24. The method ofclaim 20 wherein said printed circuit board substrate comprises anelectrical terminal and wherein said diode chip is coupled with saidprinted circuit board substrate with a bondable wire.
 25. The method ofclaim 20 wherein said lens is formed over said diode chip by a transfermold method comprising: locating said printed circuit board on atransfer mold fixture, wherein said mold fixture comprises abi-curvature lens mold; and casting an encapsulant substance into saidbi-curvature lens mold.
 26. The method of claim 25 further comprisingheat-curing said printed circuit board after forming said lens over saiddiode chip.
 27. The method of claim 20 wherein said diode chip is alight emitting diode chip.
 28. The method of claim 20 wherein said diodechip is a photo detector chip.
 29. The method of claim 20 wherein aplurality of diode chips are coupled with said printed circuit boardsubstrate, and a plurality of bi-curvature lenses are formed over saidplurality of diode chips, and wherein said method further comprisessingulating said printed circuit board into wireless communicationunits.
 30. A method for designing a lens for a light emitting diode,said method comprising: simulating a spherical bottom portion of saidlens; developing a corresponding aspheric contour for a top portion ofsaid lens; simulating a bi-curvature dome comprising said sphericalbottom portion and said aspheric top portion; simulating a radiationintensity profile through said bi-curvature dome; evaluating saidradiation intensity profile; determining whether or not said radiationintensity profile is symmetric about a maximum; if said radiationintensity profile is not symmetric about said maximum, altering aparameter of said bi-curvature dome; and repeating said simulating saidradiation intensity profile through said bi-curvature dome, evaluatingsaid radiation intensity profile, determining whether or not saidradiation intensity profile is symmetric about a maximum and alteringsaid parameter of said bi-curvature dome until said radiation intensityprofile is symmetric about a said maximum.
 31. The method of designing alens of claim 30 wherein said developing a corresponding asphericcontour for said top portion of said lens is accomplished by ray tracingtechniques.
 32. The method of designing a lens of claim 30 wherein saidsimulating said radiation intensity profile through said bi-curvaturedome is accomplished by accounting for a flux per ray analysis.